Shear stable functional fluid with low brookfield viscosity

ABSTRACT

A functional fluid of low Brookfield Viscosity comprising a mixture of at least two different base stocks with shear stable viscosity modifier polymers, and also containing performance additives.

This application claims the benefit of U.S. Ser. No. 60/497,245 filedAug. 22, 2003.

FIELD OF THE INVENTION

The invention relates to shear stable functional fluids having lowBrookfield viscosities comprising a mixture of base stocks, with shearstable viscosity modifier polymers, and also containing performanceadditives.

BACKGROUND OF THE INVENTION

Functional fluids comprise a broad range of lubricants that are used inautomotive and industrial hydraulic systems, automatic transmissions,power steering systems, shock absorber fluids, and the like. Thesefluids transmit and control power in mechanical systems, and thus musthave carefully controlled viscometric characteristics. In addition,these fluids may sometimes be formulated to provide multigradeperformance so as to ensure year round operation in variable climates.

Automatic Transmission Fluid (ATF) is one of the most common functionalfluids, and an integral part of all automatic transmissions. Automatictransmissions are used in about 80% to 90% of all vehicles in NorthAmerica and Japan and their use is becoming more commonplace in otherparts of the world. They are the most complex and costly sub-assembliesof a vehicle and the major Original Equipment Manufacturers (OEMs) havestringent specifications to control all aspects of the components thatgo into their manufacture, including the functional fluid.

An automatic transmission comprises a torque converter or clutchassemblies, gear assemblies, output drives and hydraulic systems. TheATF acts as a hydraulic fluid to transfer power from the engine via thetorque converter or clutch assembly, and to actuate complex controls toengage the gears to give the correct vehicle speed.

The fluid must have the right viscometrics at ambient start-uptemperatures, which can be as low as −40° C., while maintainingsufficient viscosity at higher operating temperatures of 100° C. ormore. ATF must also be oxidation stable since it is subjected to hightemperatures and is expected to remain in service for up to 100,000miles in some cases. In addition, frictional characteristics areimportant so as to provide smooth control of shifting with the clutchplates.

Great strides have been made in ATF additive formulation science to meetthese viscometric and oxidation requirements using solvent extractedmineral oils, commonly referred to as Group I base stocks. However, overthe past few years, with the increasing performance demands being madeon automatic transmission fluids, the use of hydrocracked base stocks,commonly referred to as Group II or Group III base stocks, have becomemore widespread. These base stocks give improved low temperatureperformance and longer oxidation life.

However most recently, the major automotive manufacturers have againincreased the demands on ATFs by moving to smaller and higherpower-density designs that have increased the need for improvedviscometrics. In particular, lower viscosity at lower operatingtemperatures is required to ensure proper hydraulic operation of thecomponents. TABLE 1 Brookfield Viscosity Limits of Major OEM ATFsPrevious Limits New or Pending Limits General Motors 20,000 cP max15,000 cP max Ford 20,000 cP max 13,000 cP max Chrysler 22,000 cP max10,000 cP max Toyota 20,000 cP max 15,000 cP max

In addition, it is expected that ATFs do not undergo excessive viscosityreduction through shearing during severe service. It is quite common forcurrent fluids to undergo 30% to 50%, or more viscosity loss during use,resulting in a kinematic viscosity for aged fluids of less than 4.5mm²/sec at 100° C. Such low viscosities can have a detrimental affect ontransmission operation because they are generally designed to operateover the life of the transmission with a fluid with substantiallyconstant viscosity at 100° C.

SUMMARY OF THE INVENTION

The present invention is directed to a functional fluid comprising:

-   -   (A) a mixture of at least two base stocks, said mixture        comprising        -   (i) at least one first base stock having a kinematic            viscosity of about 4.5 to about 8.0 mm²/sec at 100° C., a            viscosity index of at least 120 to about 160, a pour point            of about −12° C. maximum, a saturates content of greater            than about 98 mass %;        -   (ii) at least one second base stock having a kinematic            viscosity of about 2.0 to about 4.5 mm²/sec at 100° C., a            viscosity index of about 100 to about 120, a pour point of            about −12° C. maximum, a saturates content of greater than            about 98 mass %;        -   wherein the first base stock is present in the amount of            about 40 vol % to about 90 vol % based on the stock,        -   wherein the second base stock is present in the amount of            about 10 vol % to about 60 vol % based on the stock,        -   wherein the first base stock (i) and second base stock (ii)            are not the same; and    -   (B) said base oil mixture (being a blend of base stocks as        defined above) has a kinematic viscosity of about 4.0 to about        5.5 mm²/sec at 100° C., a viscosity index of about 120 to about        150, a pour point of about −12° C. maximum;    -   (C) at least one viscosity index improver having a shear        stability index (SSI) less than 35, preferably less than 25, and        more preferably less than 15, as measured in the KRL Tapered        Roller Bearing Tester according to procedure CEC-L-45-T-93, said        SSI being defined by the equation        ${SSI} = {\frac{\left( {\mu_{i} - \mu_{f}} \right)}{\left( {\mu_{i} - \mu_{0}} \right)}*100}$        where    -   μ_(i)—Initial fluid viscosity @ 100° C. (fully blended ATF)    -   μ_(f)—Final after-shear fluid viscosity @ 100° C. (fully blended        ATF)    -   μ₀—Base oil viscosity @ 100° C. (blend of two or more base        stocks without any additives)    -   (D) an additive package    -   (E) the resulting additized functional fluid having, a kinematic        viscosity of about 5.0 to about 6.5 mm²/sec at 100° C., a        viscosity index of about 120 to about 180, a pour point of about        less than −42° C. maximum, and a Brookfield viscosity of about        15,000 cP or less at −40° C.    -   (F) the resulting additized functional fluid having, an after        KRL shear parameter (SP) of about 4.9 to about 5.6 mm²/sec at        100° C., preferably about 4.95 to about 5.4 mm²/sec at 100° C.,        more preferably about 4.98 to about 5.2 mm²/sec at 100° C. as        defined by ${SP} = \frac{\left( {\mu_{f} + \mu_{0}} \right)}{2}$        where    -   μ_(f)—Final after-shear fluid viscosity @ 100° C. (fully blended        ATF)    -   μ₀—Base oil viscosity @ 100° C. (blend of two or more base        stocks without any additives)

The base stocks may be prepared by use of any of the process procedurescurrently used in the art, as well as any processes yet to be developed.It is believed the performance and function of the base stocks in thepresent invention are independent of the particular proceduraltechniques employed in the production of the base stocks. Typically basestocks are made starting with distillate from the atmosphere/vacuumpipestills and/or coker distillate, optionally subjecting suchdistillate to an aromatics removal step using an aromatics selectivesolvent such as phenol, furfural, NMP, etc. The distillate is thensubjected to hydroconversion in at least one hydroconversion zone, moretypically two zones wherein the distillate is exposed to a catalyst inthe presence of hydrogen at high temperature and pressure to effect thesaturation of aromatics, open rings and reduce sulfur and nitrogencontent.

The stream from the hydroconversion stage(s) can now optionally besubject to fractionation, a further aromatics removal step such assolvent extraction employing a selective solvent such as phenol,furfural, NMP, etc, or hydroprocessing. This stream can then besubjected to wax removal employing solvent dewaxing or catalyticdewaxing or isomerization. The stream, either before or after suchdewaxing can also be subjected to hydrofinishing to further reduce thearomatic, sulfur and nitrogen contents.

Examples of suitable processes can be found in “All HydroprocessingRoute for High Viscosity Index Lubes” Zakarian et al Energy Progress,Vol. 7, No. 1, pp. 59-64; “Hydrotreated Lube Oil Base Stocks” Cashmoreet al, SAE Paper 821235; “Lube Facility Makes High Quality Lube Oil fromLow Quality Feed” Farrell et al, Oil and Gas Journal May 19, 1986,Technology, pp. 47-51; U.S. Pat. No. 5,976,353.

Other suitable stocks include hydroisomerized waxy stocks. Suitable waxystocks include waxy petroleum stock such as gas oil, foots oil, slackwaxes, waxy raffinates, deasphalted oils, fuels hydrocracker bottoms,etc. Hydroisomerization converts the paraffinic waxy components of thesestocks into isoparaffinic hydrocarbons which is lubricating oil. Alsosuitable as waxy stocks are those produced by the Fischer Tropschprocess which catalytically converts synthesis gas, i.e., CO and H₂,into hydrocarbons. The high boiling point residues of the FischerTropsch synthesis process products are highly paraffinic waxy stocks oflow sulfur content which are also free of nitrogen, aromatics andolefinic hydrocarbons. The hydroisomerization process can be practicedon one or more waxy petroleum stocks, Fischer Tropsch wax stocks or amixture thereof. Further, other suitable stocks can includepolyalphaolefins (PAO) whose viscosities and other characteristics fallwithin the limits recited above.

The first base stock (i) and second base stock (ii) are preferablyhydrocracked stocks and hydroisomerized stocks.

The first stock employed is one or more stocks having a kinematicviscosity of at least 4.5 to about 8.0 mm²/s at 100° C., preferablyabout 4.5 to about 7.0 mm²/s at 100° C., more preferably about 5.0 toabout 7.0 mm²/s at 100° C., a viscosity index in the range of at least120 to about 160, preferably about 125 to about 150, a pour point ofless than about −12° C., preferably less than about −15° C., morepreferably less than about −18° C., and a saturates content of greaterthan about 98 mass %.

The second stock employed is one or more stocks having a kinematicviscosity of about 2.0 to about 4.5 mm²/s at 100° C., preferably about2.5 to about 4.0 mm²/s at 100° C., more preferably about 2.5 to about3.5 mm²/s at 100° C., a viscosity index in the range of about 100 toabout 120, preferably about 100 to about 115, more preferably about 100to about 110, a pour point of less than about −12° C., preferably lessthan about −15° C., more preferably less than about −18° C., and asaturates content of greater than about 98 mass %.

The base stocks are combined to produce a base oil mixture characterizedby having a kinematic viscosity of about 4.0 to about 5.5 mm²/s at 100°C., preferably at least about 4.5 to about 5.5 mm²/s at 100° C., morepreferably at least about 4.5 to about 5.0 mm²/s at 100° C., a viscosityindex of about 120 to 150, and a pour point of about −12° C. maximum. Ablend of base stocks is employed so as to insure that the base oilkinematic viscosity target is consistently met.

A viscosity index improver or mixture of viscosity index improvers maybe employed at a treat range of 0.5 vol % to 15 vol %, preferably 0.5vol % to 10 vol %, more preferably 0.5 to 5 vol %. Viscosity indeximprover may comprise any of the common chemical types used inlubricating formulations, including, but not limited topolymethacrylates, polyisobutenes, styrene, styrene-isoprene copolymer,polyisomers, polyacylates, etc., and mixtures thereof, preferablypolymethacrylate. The only requirement which must be met is that theviscosity index improver used have an SSI meeting the requirementrecited below and that the resulting formulated ATF meet the viscometricand performance characteristics established for the ATF as presentedhereafter below.

The viscosity index improvers (VII's) which are useful in the presentinvention and are preferred are the polyalkylmethacylate (PAMA)viscosity under improvers. Such VII's are typically provided as viscousconcentrates of polymer in solvent-refined carrier oil. The aforesaidtreat ranges are on an as received basis. Nonlimiting examples of PAMAsinclude those secured from RohMax® known as Viscoplex®, those formerlyknown as Acryloid® formerly supplied by Rohm and Haas Corporation, aswell as PAMA secured from Sanyo Chemical Industries known as Aclube® orSanlube®, or from Lubrizol Corp. or other sources. Suitable non-limitingexamples include VISCOPLEX® 0-030, VISCOPLEX® 0-050, VISCOPLEX® 0-101,VISCOPLEX® 0-110, VISCOPLEX® 0-111, VISCOPLEX® 0-112, VISCOPLEX® 0-113,VISCOPLEX® 0-120, VISCOPLEX® 0-400, VISCOPLEX® 8-100, VISCOPLEX® 12-291,VISCOPLEX® 12-310, Aclube® 813, Aclube® 806T, Aclube® C-728, Aclube®975, Aclube® C-813, Aclube® 812 or Lubrizol® 7720C.

The viscosity index improver will have a shear stability index (SSI) asreported in the manufacturer's literature of less than 35, preferablyless than 25, and more preferably less than 15, as measured in the KRLTapered Roller Bearing Tester according to procedure CEC-L-45-T-93, saidSSI being defined by the equation${SSI} = {\frac{\left( {\mu_{i} - \mu_{f}} \right)}{\left( {\mu_{i} - \mu_{0}} \right)}*100}$where

-   -   μ_(i)—Initial fluid viscosity @ 100° C. (fully blended ATF)    -   μ_(f)—Final after-shear fluid viscosity @ 100° C. (fully blended        ATF)    -   μ₀—Base oil viscosity @ 100° C. (blend of two or more base        stocks without any additives)

The finished functional fluid will contain a performance additivepackage. Such performance additives will be used in an amount of about 4to about 20 vol %, preferably about 5 to about 15 vol % of the totalformulated oil. Performance additives include, but are not limited to,metallic and ashless oxidation inhibitors, metallic and ashlessdispersants, metallic and ashless detergents, corrosion and rustinhibitors, metal deactivators, anti-wear agents (metallic andnon-metallic, low-ash, phosphorus-containing and non-phosphorus,sulfur-containing and non-sulfur types), extreme pressure additives(metallic and non-metallic, phosphorus-containing and non-phosphorussulfur-containing and non-sulfur types), anti-seizure agents, pour pointdepressants, wax modifiers, viscosity index improvers, viscositymodifiers, seal compatibility agents, friction modifiers, lubricityagents, anti-staining agents, chromophoric agents, defoamants,demulsifiers, and others. For a review of many commonly used additivessee Klamann in Lubricants and Related Products, Verlag Chemie, DeerfieldBeach, Fla.; ISBN 0-89573-177-0, and also Lubricant Additives by M. W.Ranney, published by Noyes Data Corporation of Parkridge, N.J. (1973)both of which are incorporated here by reference.

Antiwear additives include metal alkylthiophosphate and moreparticularly a metal dialkyldithiophosphate in which the primary metalconstituent is zinc, or zinc dialkyldithiophosphate (ZDDP). ZDDPcompounds generally are of the formula Zn[SP(S)(OR¹)(OR²)]₂ where R¹ andR² are C₁-C₁₈ alkyl groups, preferably C₂-C₁₂ alkyl groups. These alkylgroups may be straight chain or branched. These ZDDP type antiwearadditives are typically used in amounts of from about 0.4 wt % to about1.4 wt %, but more or less can be used at the discretion of thepractitioner.

Non-phosphorous antiwear additives can also be used and they includesulfurized olefins.

Polysulfides of thiophosphorous acids and thiophosphorus acid esters,phosphorothenyl desulfides, alkylthiocarbamoyl compounds in combinationwith molybdenum compounds and a phosphorus ester are also usefulantiwear additives as are carbamate, thiocarbamate andthiocarbamate/molybdenum complexes such as moly-sulfuralkyldithiocarbamate complexes, as well as esters of glycerol. Further,mixtures of ZDDP and thiodixanthogen compounds can also improve antiwearproperties.

Antiwear additives may be used in amounts of from about 0.01 to 6 wt %,preferably about 0.01 to 2 wt %.

Antioxidants include hindered phenols and maybe ashless (metal free) orneutral or basis metal salts of phenolic compounds (ashed). Hinderedphenols contain one or more hydroxyl groups of which one or more issterically hindered. Bis-phenolic antioxidants can also be used, e.g.,ortho-coupled bis-phenols such as 2, 2′-bis(6-t-butyl-4-heplyl phenol);2,2′-bis(6-t-butyl-4-octyl phenyl) and paracoupled bis-phenols such as4,4′-bis(2-6-di-t-butyl phenol) and 4,4′methylene-bis(2,6-di-t-butylphenol).

Non-phenolic antioxidants include aromatic amine antioxidants and thesemay be used either alone or in combination with phenolic antioxidants.Aminic antioxidants include diphenylamines, phenyl naphthylamines,pheno-thiazines, imidodibenzyls and diphenyl phenylene diamines.Mixtures of two or more aminic antioxidants can be used.

Sulfurized alkyl phenols and alkali or alkaline earth metal saltsthereof are also useful antioxidants.

Oil soluble copper compounds such as copper dihydrocarbyl thio- ordithio-phosphates and copper salts of carboxylic acid are alsoantioxidants, as are copper dithiocarbamate sulphonates, phenates andacetylacetonates. Basic neutral or acidic copper Cu(I) and or Cu(II)salts derived from alkenyl succinic acids or anhydrides can also beused.

Antioxidants are typically used in an amount of about 0.01 to 5 wt %,preferably about 0.01 to 2 wt %.

Useful detergents can be neutral, mildly overbased or highly overbased.At least some overt acid detergent is desirable. The total base numberof the detergent can range as high as 450 mgKOH/g or higher. A mixtureof detergents of different total base numbers is preferred. Detergentsinclude the alkali or alkaline earth metal salts of sulfates, phenates,carboxylates, phosphates and salicylites and preferred detergentsinclude calcium or magnesium phenates, sulfonates and salicylates,including the borated versions of these materials.

Detergents are used in an amount of about 0.01 to 6 wt %, preferablyabout 0.1 to 4 wt %.

Dispersants function by keeping byproducts and decomposition products insolution, thereby reducing their deposition on metal surfaces.Dispersants may be ashless or ash forming, and may also be borated, theashless borated or unborated type being preferred.

Dispersants include phenates, sulfonates, sulfurized phenates,salicylates, naphthenates, stearates, carbamates, thiocarbamates andphosphorus derivatives. A particularly useful class of dispersants arealkenylsuccinic derivatives, typically produced by the reaction of along chain substituted alkenyl succinic compound, usually a substitutedsuccinic acid or anhydride, preferably the anhydrate, with a polyhydroxyor polyamine compound. The long chain group substituted in the alkenylsuccinic compound is normally a polyiso-butylene group having anywherefrom 35 to 100 to 150 or more carbon atoms, more usually at least about50 carbon atoms.

Hydrocarbyl substituted succinic acid/acid anhydride compounds useful asdispersants include the succinimides, succinate esters and succinateester amides.

The succinimides are formed by the condensation reaction between alkenylsuccinic anhydrides and amines. The succinate esters are formed by thecondensation reaction between alkenyl succinic anhydrides and alcoholsor polyols. The succinate ester amides are formed by the condensationreaction between alkenyl succinic anhydrides and alkanol amines.

The hydrocarbyl substituted succinic acid/acid anhydride compounds canbe post treated with various reagents such as sulfur, oxygen,formaldehyde, carboxylic acids (such as oleic acid) and boron compounds.The dispersants can be borated with from about 0.1 to about 5 moles ofboron per mole of dispersant reaction product. Preferred are the boratedmono-succinimide, bis-succinimides and mixtures thereof, wherein thehydrocarbyl substitutent is a polyisobutylene having an Mn of from about500 to 5000, or a mixture of such hydrocarbyl groups.

Other dispersants are the Mannich base dispersants made by the reactionof alkylphenols, formaldehyde and amines. See U.S. Pat. No. 4,767,551incorporated herein by reference in its entirety.

Suitable dispersants also include oxygen containing compounds such aspolyether compounds, polycarbonate compounds and/or polycarbonylcompounds.

Dispersants may be used in an amount of about 0.1 to 20 wt %, preferablyabout 0.1 to 8 wt %.

Friction modifiers, also known as lubricity agents or oiliness agentsinclude metal-containing compounds as well as ashless compounds, andmixtures thereof. Metal-containing friction modifiers may include metalsalts or metal-ligand complexes where the metals may include alkali,alkaline earth, or transition group metals. Such metal-containingfriction modifiers may also have low-ash characteristics. Transitionmetals may include Mo, Sb, Sn, Fe, Cu, Zn, and others. Ligands mayinclude hydrocarbyl derivate of alcohols, polyols, glycerols, partialester glycerols, thiols, carboxylates, carbamates, thiocarbamates,dithiocarbamates, phosphates, thiophosphates, dithiophosphates, amides,imides, amines, thiazoles, thiadiazoles, dithiazoles, diazoles,triazoles, and other polar functional groups containing effectiveamounts of O, N, S, or P, individually or in combination. Particularlypreferred are Mo-dithiocarbamates (Mo(DTC)), Mo-dithiophosphates(Mo(DTFP), Mo-amines (Mo(Am)), Mo-alcoholates, Mo-alcohol-amides, etc.

Ashless friction modifiers include hydroxyl-containing hydrocarbyl baseoils, glycerides, partial glycerides, glyceride derivatives and thelike, as well as salts (both ash-containing and ashless derivatives) offatty acids, fatty alcohols, fatty amides, fatty esters,hydroxyl-containing carboxylates, and comparable synthetic long chainhydrocarbyl acids, alcohols, amides, esters, hydroxy carboxylates, etc.Also useful are fatty organic acids, fatty amines and sulfurized fattyacids.

Friction modifiers are used in amounts of from about 0.01 to 15 wt %,preferably 0.01 to 10 wt %, more preferably 0.1 to 5 wt %. The amount ofmolybdenum containing friction modifiers is usually expressed in termsof molybdenum metal concentrations, the amount usually being in therange of about 10 to 3,000 ppm or more, preferably about 20-2,000 ppm,more preferably about 30-1,000 ppm.

Pour point depressants include polymethacrylates, polyacrylates,polyarylamides, condensation products of haloparaffin waxes and aromaticcompounds, vinyl carboxylate polymers, and terpolymers ofdialkylfumarates, vinyl esters of fatty acids and allyl vinyl ethers.They have be used in an amount of about 0.01 to 5 wt %, preferably about0.01 to 1.5 wt %.

Corrosion inhibitors are used to reduce the degradation of metallicparts that are in contact with the lubricating oil composition. Suitablecorrosion inhibitors include thiadizoles and thiadiazoles. They are usedin an amount of about 0.01 to 5 wt %, preferably about 0.01 to 1.5 wt %.

Seal compatibility agents, also known as seal swell agents, includeorganic phosphates, aromatic esters, aromatic hydrocarbons, esters suchas butylbenzyl phthalate, and polybutenyl succinic anhydrides. They areused in an amount of about 0.01 to 3 wt %, preferably about 0.01 to 2 wt%.

Anti-foam agents include silicones and organic polymers such aspolysiloxane, silicone oils or polydimethylsiloxane. They are used intrace amounts, usually less than 1 wt % and preferably less than 0.01 wt%.

Anti-rust additives, also known as corrosion inhibitors, include polarcompounds that wet the metal surface protecting it with a film of oil,compounds that absorb water by incorporating it into a water-in-oilemulsion so that the oil and not the water touches the metal surface,and compounds that chemically adhere to the metal to producenon-reactive surfaces. Examples include zinc dithiophosphate, metalphenalates basic metal sulfonates, fatty acids and amines. They may beused in amounts of about 0.01 to 5 wt %, preferably about 0.01 to 1.5 wt%.

Additional types of additives may be further incorporated into lubricantcompositions or functional fluids of this invention, and may include oneor more additives such as, or example, demulsifiers, solubilizers,fluidity agents, coloring agents, chromophoric agents, and the like, asrequired. Further, each additive type may include individual additivesor mixtures of additive.

The additives either individually or as a package can be marketed eitheras 100% active ingredient materials or as concentrates in diluent oil.The amount of diluent oil associated with the additive(s), therefore,can range from zero to about 40 vol %. The diluent oil embraces any oilof sufficient viscosity and solvency being such that the finalformulated ATF performance characteristics are within the limits recitedherein, and would include any naphthenic, paraffinic or aromatic oil,e.g., any suitable Group I, Group II, Group III, Group IV or Group V oil(term of oil known to those skilled in the art).

The final additized functional fluid is characterized as having akinematic viscosity of about 5.0 to about 6.5 mm²/s at 100° C.,preferably about 5.3 to about 6.4 mm²/s at 100° C., a viscosity index ofabout 120 to about 180, a pour point of less than about −42° C. maximumand a Brookfield viscosity about 15,000 cP or less at −40° C.

The invention will be further explained by and understood by referenceto the following non-limiting examples, see Table 2.

In Table 2 base stocks Q, A, B, C, D, X, Y and Z are hydrocracked basestocks. Base stocks E and F are the products of the hydroisomerizationof waxy feed stocks. Base stock E is hydroisomerized waxy stock from apetroleum source, slack wax, while base stock F in hydroisomerizedFischer Tropsch wax. Fischer Tropsch waxes are the waxy, high boilingresidue of the Fischer Tropsch process which converts synthesis gas (COand H₂) into hydrocarbons. Fischer Tropsch waxes are highly paraffinichydrocarbons with very low sulfur content. The specification for eachstock is recited in Table 2. TABLE 2 SHEAR STABLE FUNCTIONAL FLUID WITHLOW BROOKFIELD VISCOSITY First Base Stock Second Base Stock KV100 KV40KV100 KV40 Code (mm²/s) (mm²/s) VI vol % Code (mm²/s) (mm²/s) VI vol %Comparative Example A Q 4.593 22.88 117 100.000 — — — — 0.000 B A 5.36229.26 118 73.579 X 3.109 12.56 107 26.421 C A 5.362 29.26 118 81.275 Y2.557 9.373 101 18.725 D A 5.362 29.26 118 74.530 Z 3.052 12.21 10725.470 E C 5.053 25.74 126 100.000 — — — — 0.000 F D 6.433 36.29 13056.858 X 3.109 12.56 107 43.142 Inventive Example  1 B 6.047 33.34 12961.554 X 3.109 12.56 107 38.446  2 B 6.047 33.34 129 71.392 Y 2.5579.373 101 28.608  3 B 6.047 33.34 129 62.722 Z 3.052 12.21 107 37.278  4C 5.053 25.74 126 81.722 X 3.109 12.56 107 18.278  5 C 5.053 25.74 12687.448 Y 2.557 9.373 101 12.552  6 C 5.053 25.74 126 82.455 Z 3.05212.21 107 17.545  7 D 6.433 36.29 130 56.813 X 3.109 12.56 107 43.187  8D 6.433 36.29 130 67.223 Y 2.557 9.373 101 32.777  9 D 6.433 36.29 13058.027 Z 3.052 12.21 107 41.973 10 E 6.621 35.05 147 55.014 X 3.10912.56 107 44.986 11 E 6.621 35.05 147 65.608 Y 2.557 9.373 101 34.392 12E 6.621 35.05 147 56.251 Z 3.052 12.21 107 43.749 13 F 6.062 30.83 14861.336 X 3.109 12.56 107 38.664 14 F 6.062 30.83 148 71.208 Y 2.5579.373 101 28.792 15 F 6.062 30.83 148 62.516 Z 3.052 12.21 107 37.484Base Stock Blend ATF Blend KV100 KV40 KV100 KV40 BF Code (mm²/s) (mm²/s)VI (mm²/s) (mm²/s) VI (cP@ −40° C.) Comparative Example A Q 4.593 22.88117 6.174 — — 41,391 B AX 4.588 22.93 116 — — — 16,297 C AY 4.585 22.93116 6.199 32.20 144 16,836 D AZ 4.588 22.92 116 — — — 17,436 E C 5.05325.74 126 6.189 32.57 141 17,466 F DX 4.582 22.08 124 6.292 33.58 14022,245 Inventive Example  1 BX 4.585 22.17 124 6.204 31.37 151 13,357  2BY 4.580 22.06 124 6.222 31.46 151 14,317  3 BZ 4.585 22.16 124 — — —14,657  4 CX 4.590 22.32 122 6.149 31.20 149 13,117  5 CY 4.588 22.28123 6.189 31.40 150 12,927  6 CZ 4.590 22.31 123 — — — 14,377  7 DX4.580 22.07 124 6.269 31.53 153 11,798  8 DY 4.574 21.92 125 6.284 31.54154 12,197  9 DZ 4.580 22.04 125 6.252 31.66 151 12,907 10 EX 4.58321.29 134 6.302 30.75 161 10,898 11 EY 4.577 21.00 137 6.305 30.48 16311,098 12 EZ 4.583 21.25 134 6.273 30.81 159 11,967 13 FX 4.585 21.19135 — — — 11,018 14 FY 4.580 20.93 138 6.213 29.95 163 9,758 15 FZ 4.58421.16 136 — — — 10,138

ATF blends were made using various “first base stocks” and “second basestocks”, along with a VI improver secured from an independent source andis believed to be RohMax VISCOPLEX® 0-050 having a SSI measured by thetechnique recited herein of about 8 and performance additives. Thekinematic viscosity of the blended mixture of the “first and second basestocks” was targeted to be about 4.6 mm²/s at 100° C., except whereotherwise indicated as in Comparative Example E. The VI improver treatrate was 5 vol % as received, active ingredient level ˜40-75%, except inComparative Example E wherein the VI improver treat rate was 2.75 vol %as received, and the treat rate of the performance additives was about 8vol % as received and were kept constant in the examples and comparativeexamples unless otherwise indicated. In Comparative Example F adifferent type of VI improver was used, a polyisobutylene VI improveremployed at a treat rate of 3.5% vol %, as received (90% activeingredient).

COMPARATIVE EXAMPLE A

ATF blend “A” comprised only a “first base stock” having a viscosityindex (VI) of 117. The Brookfield was 41,391 mPa.s at −40° C. TheBrookfield was well above the specification target of 15,000 cP.

COMPARATIVE EXAMPLES B, C, D

ATF blends “B”, “C” and “D” comprised a “first base stock” having aviscosity index (VI) of 118 and three different “second base stocks”having a VI of 107, 101 and 107 respectively. The resulting “base oil”blends had a VI of 116, 116 and 116 respectively. The Brookfield for thethree ATFs were 16,297 and 16,836 and 17,436 cP respectively. TheBrookfields were above the specification target of 15,000 cP.

COMPARATIVE EXAMPLE E

ATF blend “E” comprises a single “first base stock” having a viscosityindex of 126 and a KV at 100° C. of 5.053. On its face, therefor, thissingle base stock would appear to meet the viscometric requirementsestablished for the base stock blend of the present invention (thetarget KV at 100° C. and VI for blended oils being 4.0 to about 5.5mm²/s and about 120 to 150 respectively). The ATF made using only thesingle base stock had Brookfield Viscosity at −40° C. of 17,466 cP, wellabove the specification target of 15,000 cP. This demonstrates that ablend of base stocks is necessary to achieve a final ATF formulationmeeting the taught viscometric specification.

COMPARATIVE EXAMPLE F

ATF blend F comprised a “first base stock” having a viscosity index (VI)of 130 and a “second base stock” having a VI of 107. The resulting “baseoil” had a VI of 124 and a KV at 100° C. of 4.582. A PIB VI improver wasemployed at a treat rate of 3.5 vol %, as received (90% activeingredient). The VI improver had an SSI, as measured by the KRLtechnique recited herein, of about 9, and a molecular weight of about2,000. The Brookfield viscosity of the ATF was 22,245 cP @ −40° C., wellabove the specification target of 15,000 cP.

INVENTIVE EXAMPLES 1, 2, 3

ATF blends “1”, “2” and “3” comprised a “first base stock” having aviscosity index (VI) of 129 and three different “second base stocks”having a VI of 107, 101 and 107 respectively. The resulting “base oil”blends had a VI of 124, 124 and 124 respectively. The Brookfield for thethree ATFs were 13,357 and 14,317 and 14,657 cP respectively. TheBrookfields met the specification target of 15,000 cP.

INVENTIVE EXAMPLES 4, 5, 6

ATF blends “4”, “5” and “6” comprised a “first base stock” having aviscosity index (VI) of 126 and three different “second base stocks”having a VI of 107, 101 and 107 respectively. The resulting “base oil”blends had a VI of 122, 123 and 123 respectively. The Brookfield for thethree ATFs were 13,117 and 12,927 and 14,377 cP respectively. TheBrookfields met the specification target of 15,000 cP.

INVENTIVE EXAMPLES 7, 8, 9

ATF blends “7”, “8” and “9” comprised a “first base stock” having aviscosity index (VI) of 130 and three different “second base stocks”having a VI of 107, 101 and 107 respectively. The resulting “base oil”blends had a VI of 124, 125 and 125 respectively. The Brookfield for thethree ATFs were 11,798 and 12,197 and 12,907 cP respectively. TheBrookfields met the specification target of 15,000 cP.

INVENTIVE EXAMPLES 10, 11, 12

ATF blends “10”, “11” and “12” comprised a “first base stock” having aviscosity index (VI) of 147 and three different “second base stocks”having a VI of 107, 101 and 107 respectively. The resulting “base oil”blends had a VI of 134, 137 and 134 respectively. The Brookfield for thethree ATFs were 10,898 and 11,098 and 11,967 cP respectively. TheBrookfields met the specification target of 15,000 cP.

INVENTIVE EXAMPLES 13, 14, 15

ATF blends “13”, “14” and “15” comprised a “first base stock” having aviscosity index (VI) of 148 and three different “second base stocks”having a VI of 107, 101 and 107 respectively. The resulting “base oil”blends had a VI of 135, 138 and 136 respectively. The Brookfield for thethree ATFs were 11,018 and 9,758 and 10,138 cP respectively. TheBrookfields met the specification target of 15,000 cP.

Comparative Examples A to D demonstrate that a blend of various “firstbase stocks” and “second base stocks”, having a resultant “base oil”viscosity index of less than about 120 gave a finished ATF Brookfield ofgreater than the target of 15,000 cP at −40° C.

Comparative Example E demonstrates that an ATF formulated from a singlebase stock, even a stock which by itself meets the viscometricproperties required of the base stock blend (KV100 between 4.0-5.5, VIof 120-150, pour point of −12° C. maximum), does not meet theviscometric property requirement for the finished AFT, having a finishedATF Brookfield Viscosity of greater than the target of 15,000 cP at −40°C.

Inventive Examples 1 to 15 demonstrate that a blend of various “firstbase stocks” and “second base stocks”, having a resultant “base oil”viscosity index of about 120 or greater gave a finished ATF Brookfieldof less than 15,000 cP at −40° C.

The shear stability attributes of this invention can be illustrated bythe following non-limiting examples. A blend was made according to therecipe shown in Table 3 below. The kinematic viscosity before shear was5.58 mm²/s at 100° C. The after shear viscosity was 5.50 mm²/s at 100°C. Using the Shear Stability Index equation presented above, the SSI ofthe viscosity index improver was determined to be 8. The Shear Parameterusing the SP equation above was calculated to be 5.05. TABLE 3 Vol %First base stock (“D”) 51.8 Second base stock (“X”) 39.3 Viscosity IndexImprover 1.5 Additive Package 7.4 Result Kinematic Viscosity, mm²/s at100° C. 5.58 (fluid before KRL shear) Kinematic Viscosity, mm²/s at 100°C. 5.50 (fluid after 40 hours KRL shear) Shear Stability Index (SSI)(measured) 8 Base Oil Viscosity, mm²/s at 100° C. 4.59 Shear Parameter,mm²/s at 100° C. 5.05 Brookfield Viscosity, cP at mm²/s at 100° C.12,750

The SSI equation given above can be algebraically rearranged to give$\mu_{f} = {\mu_{i} - \left\lbrack {\frac{SSI}{100}*\left( {\mu_{i} - \mu_{0}} \right)} \right\rbrack}$Thus the ATF after shear viscosity can be calculated by knowing the ATFinitial viscosity, the base oil viscosity, and the shear stability index(SSI) for a given viscosity index improver polymer. Calculations usingthis equation are shown in Table 4.

The first row in Table 4 is the actual experimental data from Table 3,recorded here for comparative purposes for the calculations that aregiven in the following rows.

Assuming an SSI of 15, and using the ATF before shear viscosity (5.58)and base oil viscosity (4.59) from Table 3, the after shear viscosity ofthe oil if one used viscosity index improver having a SSI of 15 can becalculated to be 5.43 cSt. Using the SP equation above, the shearparameter is calculated to be 5.01 cSt.

Similarly, Table 4 shows the calculated after shear viscosities andshear parameters for different VII having a range of assumed SSI valuesof 25, 35, 55 and 75.

The data in Table 4 shows that an SSI less than 35, more preferably lessthan 25 and most preferably less than 15 is necessary to meet the targetshear parameter requirements for the ATF. TABLE 4 Shear Stability IndexATF After Shear ATF Shear Parameter (SSI) Viscosity @ 100° C. @ 100° C.8 5.50 5.05 15 5.43 5.01 25 5.33 4.96 35 5.23 4.91 55 5.04 4.81 75 4.844.71ATF Before Shear Viscosity @ 100° C. (mm²/s) = 5.58Base Oil Blend Viscosity @ 100° C. (mm²/s) = 4.59

1. A functional fluid comprising: (A) a mixture of at least two basestocks, said mixture comprising (i) at least one first base stock havinga kinematic viscosity of at least 4.5 to about 8.0 mm²/sec at 100° C., aviscosity index of at least 120 to about 160, a pour point of about −12°C. maximum, a saturates content of greater than about 98 mass %; (ii) atleast one second base stock having a kinematic viscosity of about 2.0 toabout 4.5 mm²/sec at 100° C., a viscosity index of about 100 to about120, a pour point of about −12° C. maximum, a saturates content ofgreater than about 98 mass %; wherein the first base stock is present inthe amount of about 40 vol % to about 90 vol % based on the stock,wherein the second base stock is present in the amount of about 10 vol %to about 60 vol % based on the stock, wherein the first base stock (i)and second base stock (ii) are not the same; and (B) said base oilmixture (being a blend of base stocks as defined above) has a kinematicviscosity of about 4.0 to about 5.5 mm²/sec at 100° C., a viscosityindex of about 120 to about 150, a pour point of about −12° C. maximum;(C) at least one viscosity index improver having a shear stability index(SSI) less than 35, as measured in the KRL Tapered Roller Bearing Testeraccording to procedure CEC-L-45-T-93, said SSI being defined by theequation${SSI} = {\frac{\left( {\mu_{i} - \mu_{f}} \right)}{\left( {\mu_{i} - \mu_{0}} \right)}*100}$where μ_(i)—Initial fluid viscosity @ 100° C. (fully blended ATF)μ_(f)—Final after-shear fluid viscosity @ 100° C. (fully blended ATF)μ₀—Base oil viscosity @ 100° C. (blend of two or more base stockswithout any additives); (D) an additive package; (E) the resultingadditized functional fluid having, a kinematic viscosity of about 5.0 toabout 6.5 mm²/sec at 100° C., a viscosity index of about 120 to about180, a pour point of about less than −42° C. maximum, and a Brookfieldviscosity of about 15,000 cP or less at −40° C.; (F) the resultingadditized functional fluid having, an after KRL shear parameter (SP) ofabout 4.9 to about 5.6 mm²/sec at 100° C. as defined by${SP} = \frac{\left( {\mu_{f} + \mu_{0}} \right)}{2}$ where μ_(f)—Finalafter-shear fluid viscosity @ 100 ° C. (fully blended ATF) μ₀—Base oilviscosity @ 100 ° C. (blend of two or more base stocks without anyadditives).
 2. The functional fluid of claim 1 wherein base stock (i)has a kinematic viscosity of about 4.5 to about 7.0 mm²/s at 100° C., aviscosity index in the range of about 125 to about 150, a pour point ofless than about −15° C.
 3. The functional fluid of claim 1 wherein basestock (i) has a kinematic viscosity of about 5.0 to about 7.0 mm²/s at100° C., a viscosity index in the range of about 125 to about 150, apour point of less than −18° C.
 4. The functional fluid of claim 1wherein base stock (ii) has a kinematic viscosity of about 2.5 to about4.0 mm²/s at 100° C., a viscosity index in the range of about 100 toabout 115, a pour point of less than −15° C.
 5. The functional fluid ofclaim 2 wherein base stock (ii) has a kinematic viscosity of about 2.5to about 4.0 mm²/s at 100° C., a viscosity index in the range of about100 to about 115, a pour point of less than −15° C.
 6. The functionalfluid of claim 3 wherein base stock (ii) has a kinematic viscosity ofabout 2.5 to about 4.0 mm²/s at 100° C., a viscosity index in the rangeof about 100 to about 115, and a pour point of less than −15° C.
 7. Thefunctional fluid of claim 1 wherein base stock (ii) has a kinematicviscosity of about 2.5 to about 3.5 mm²/s at 100° C., a viscosity indexin the range of about 100 to about 110 and a pour point of less than−18° C.
 8. The functional fluid of claim 2 wherein base stock (ii) has akinematic viscosity of about 2.5 to about 3.5 mm²/s at 100° C., aviscosity index in the range of about 100 to 110 and a pour point ofless than −18° C.
 9. The functional fluid of claim 3 wherein base stock(ii) has a kinematic viscosity of about 2.5 to about 3.5 mm²/s at 100°C., a viscosity index in the range of about 100 to 110, and a pour pointof less than −18° C.
 10. The functional fluid of claims 1, 2, 3, 4, 5,6, 7, 8 or 9 wherein the viscosity index improver has a shear stabilityindex (SSI) of less than
 25. 11. The functional fluid of claim 1, 2,3,4, 5, 6, 7, 8 or 9 wherein the additized functional fluid has an afterKRL shear parameter (SP) of about 4.95 to about 5.4 mm²/s at 100° C. 12.The functional fluid of claim 10 wherein the additized functional fluidhas an after KRL shear parameter (SP) of about 4.95 to about 5.4 mm²/sat 100° C.
 13. The functional fluid of claim 1, 2, 3, 4, 5, 6, 7, 8 or 9wherein the additized functional fluid has an after KRL shear parameter(SP) of about 4.98 to about 5.2 mm²/s at 100° C.
 14. The functionalfluid of claim 10 wherein the additized functional fluid has an afterKRL shear parameter (SP) of about 4.98 to about 5.2 mm²/s at 100° C. 15.The functional fluid of claim 1, 2, 3, 4, 5, 6, 7, 8 or 9 wherein thebase oil mixture (B) has a kinematic viscosity of at least about 4.5 toabout 5.5 mm²/s at 100° C.
 16. The functional fluid of claim 10 whereinthe base oil mixture (B) has a kinematic viscosity of at least about 4.5to about 5.5 mm²/s at 100° C.
 17. The functional fluid of claim 11wherein the base oil mixture (B) has a kinematic viscosity of at leastabout 4.5 to about 5.5 mm²/s at 100° C.
 18. The functional fluid ofclaim 12 wherein the base oil mixture (B) has a kinematic viscosity ofat least about 4.5 to about 5.5 mm²/s at 100° C.
 19. The functionalfluid of claim 13 wherein the base oil mixture (B) has a kinematicviscosity of at least about 4.5 to about 5.5 mm²/s at 100° C.
 20. Thefunctional fluid of claim 14 wherein the base oil mixture (B) has akinematic viscosity of at least about 4.5 to about 5.5 mm²/s at 100° C.21. The functional fluid of claim 1 wherein the viscosity index improveris a PAMA.